Electromagnetic Immunity; Esd - Zapi EPS-AC0 SWs&ENC User Manual

7.9.2 Electromagnetic Immunity

The electromagnetic immunity concerns the susceptibility of the controller to
external electromagnetic fields and their influence on its correct work made.
These tests are carried out at determined levels of electromagnetic fields, to
simulate external undesired disturbances and verify the electronic device response.
Here are some suggestions to improve the electromagnetic immunity:
1) SHIELDING: enclosing controller and wiring when possible on a shielded box;
using shielded cables.
2) LAYOUT: hide the exposed wires, which are connected to the controller, behind
metallic part working like natural barriers.
3) FERRITES: embrace the exposed wires, connected to the controller, with a split
or solid ferrite.
4) BY-PASS CAPACITOR: connect an interference suppression capacitor (Y type)
between the minus battery and the truck frame, as close as possible to the
controller.

7.9.3 ESD

When an accumulation of charge occurs in a part insulated from the ground, it may
discharging in a shot when turning in contact with a part having different potential.
This phenomenon is called Electrostatic Discharge (ESD).
In forklift trucks applications, special attention should be adopted for avoiding ESD.
The main rule is that it is always much easier and cheaper to avoid ESD from
being generated, than to increase the level of immunity of the electronic
devices.
ESD happens when there is a rapid transfer from a charged part to another. This
rapid transfer has, in turn, two important effects:
5) It can determine, by induction, disturbs on the signal wiring and thus create
malfunctions. This effect is particularly critical in modern machines, with CAN
Bus communications, which are spread everywhere on the truck and which
carry critical information.
6) In the worst case and when the amount of charge is very high, the discharge
process can determine failures in the electronic devices; the type of failure can
vary from an intermittently malfunction to a completely failure of the electronic
device.
Three ways can be followed to prevent damages from ESD:
1) INSULATION: To prevent the controller from ESD, it is necessary to consider
that the operator is most of the time the source of ESD. When it gets in touch
with a device on the dashboard having metallic head terminal, the accumulated
charge will be directed from the head terminal to the wires of the device towards
the other units in the truck (e.g. the CAN Bus wires or the wires of the stepper
motor on the dashboard could be the transmission mean). As consequence a
huge inrush current will be generated getting the controller cut off or damaged.
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To prevent ESD risk it is necessary to avoid that the devices connected to the
CAN communication system have exposed metallic head terminals. The
operator shall not get in touch with any metallic part of the devices CAN Bus
connected.
2) GROUNDING: when a complete isolation cannot be achieved, a good
grounding can divert the discharge current trough a "safe" path; the frame of a
truck can work like a "local earth ground", absorbing excess charge.
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